Objective:To investigate the influence of intraoperative intravenous magnesium sulfate on muscle relaxation effects of vecuronium,and evaluate its safety. Methods:Sixty patients underwent elective lumbar discectomy and internal fixation were randomly divided into two groups with 30 cases in each group. After induction of anesthesia,40 mg/kg of magnesium sulfate was given in group A through intravenous infusion,group B received the same volume of saline. Propofol (3.0~3.5 μg/ml) and remifentanil (3.0~4.0 ng/ml) were injected by plasma concentrations target-controlled infusion to maintain BIS at 45~55. Vecuronium was administrated with muscle relaxants integrated closed-loop target controlled injection system,and TOF was set to 0. Serum Mg2+,Ca2+ and K+ concentration were detected at four time points:preoperative (t1),10 min (t2) and 60 min (t3) after medication of magnesium or placebo,and t4 when vecuronium was disabled. Heart rate (HR) and mean arterial pressure (MAP) were accessed 5 min after medication of magnesium or placebo. The time of T70% (TOF recover up to 70%) and the total dosage of vecuronium were recorded. Results:Serum concentration of Mg2+ reached a maximum (1.33 ± 0.19 mmol/L) at t2,and declined gradually through the passing of operation time in group A (P < 0.05),and still higher than that in group B at t3 and t4 (P < 0.05). Serum concentration of Ca2+ and K+,as well as HR and MAP showed no significant difference between the two groups (P > 0.05). The dosage of vecuronium was (3.22 ± 0.57) μg/(kg-min) in group A,significantly less than that in group B (3.81 ± 0.58) μg/(kg-min) (P = 0.0002);T70% in group A and group B were (26.3 ± 3.6) min and (28.7 ± 4.3) min,respectively,the difference was statistically significant (P = 0.0225). Conclusion:Intravenous injection of 40 mg/kg magnesium sulfate could enhance muscle relaxation effects of vecuronium,reduce the dosage and shorten neuromuscular recovery time,and has no significant effect on serum concentration of Ca2+,K+ and hemodynamics.